The present invention relates to a method and an apparatus for electrically controlling a flow of material, wherein a single- or multi-component, essentially polymer-based material, such as plastics, elastomer or the like, is charged electrically and sprayed in an electrical field to a three-dimensional mould/target.
At present, it is conventional to employ so-called electrostatic coating e.g. in automotive painting. This application is generally carried out by using metal-based coating materials, whose electrical charge and spraying in an electrical field can be achieved in the discussed application in a sufficiently homogeneous manner, such that the automobile is provided all over with a sufficiently thick layer of paint. However, the above type processing is inconvenient to carry out in practice with a sufficient reliability, especially when used in connection with plastic-based materials because of a poor applicability of this type of materials to the discussed processing. On the other hand, it is perfectly well known to provide the plastics to be sprayed with an electrical charge by using suitable polarity/resistivity regulating materials, such as chlorine-/glycol-based materials or the like. Despite this, however, this type of electrical processing of a plastic material has not been possible to perform thus far with a sufficient reliability, which is why e.g. conventional thin-walled ordinary articles, such as gloves, condoms or the like, must still be manufactured largely by using a traditional dip process.
On the other hand, the International patent publication WO 94/22594 discloses a process for coating especially objects with varying shapes, which is based on the fact that a multi-component material, one comprising a cold curing and inert, e.g. solvent-free resin, is electrostatically applied to a surface of an object, whereafter at least one fluid material is sprayed onto the resin before it has cured.
The cited publication does not present any concrete solution for performing the above-described task, as it mostly discloses various alternative working principles for providing a coating. On the basis of technology described in the cited publication, it is not possible in practice to make sure that especially a flow of resin-based, electrically processible material be applied particularly to a multi-dimensionally shaped article in such a way that each area/point of the article would be provided exactly with a desired material thickness, which thus remains to be a central problem, especially in terms of processing resin- or plastic-based materials electrically.
An object of this intention is to provide a decisive remedy for the above-described problems and hence to raise substantially the available prior art. In order to achieve this object, a method of the invention is principally characterized in that the method makes use of a mould/target set at an electric potential, which is provided with two or more treatment blocks to be set at voltage levels different from each other, especially for coordinating the courses of sprayed material particles and the electrical field affecting the same, in such a manner that each section/area of the mould/target surface forms a material layer of desirable thickness in a spraying cycle II.
The method of the invention offers some major advantages, including e.g. its technical functionality and applicability, by virtue of which it is practically for the first time possible to provide a sufficiently reliable result in most diverse applications, even when using a plastic-based manufacturing material in connection with the above type of electrical processing. Usefulness of the method is based on the fact that a mould of the invention, by virtue of mathematically determined unequal voltage levels in the treatment blocks included therein, enables a precise determination of material thickness in such a way that the end result of actual processing is exactly as desired. The method of the invention also makes it possible that a target to be processed, such as an object to be coated or an article to be manufactured therefrom, be intentionally provided in desired areas with substantially unequal wall thicknesses. Furthermore, it is basically possible to apply the method in a traditional fashion, e.g. electrostatically, such that the predetermined voltage levels in the various processing blocks of a mould are kept essentially constant through the entire spraying cycle. On the other hand, it is also possible in this context to make use of a dynamically controlled spraying process in such a manner that one or several process parameters are changed continuously or periodically during a spraying cycle.
Preferred applications for the method of the invention are set forth in the non-independent claims directed to a method.
The invention relates also to an apparatus operating in accordance with a method for electrically controlling a flow of material, wherein a single- or multi-component, essentially polymer-based material or the like, is charged electrically (I) and sprayed (II) in an electrical field (E) to a three dimensional mould (2)/target (3), characterized in, that the method makes use of the mould (2)/target(3) set at an electric potential, which is provided with two or more treatment blocks (Li) to be set at voltage levels different from each other, especially for coordinating the courses of sprayed material particles and the electrical field (E) affecting the same, in such a manner that each section/area of the mould/target surface forms a material layer of desirable thickness in the spraying cycle (II).
The most important advantages offered by the apparatus of the invention include technical reliability in its operation and function as well as usefulness for the most diverse applications. First of all, the fundamental concept of the apparatus of the invention lies in the fact that a control unit included therein enables the setting of separate processing blocks included in a mould at e.g. mathematically predetermined voltage levels, such that the actual spraying process is capable of producing an absolutely controlled flow of material to each surface/wall of a mould/target to be treated/manufactured at a given time. Depending on the nature of a process, it is possible to arrange the control unit, e.g. according to a basically traditional approach, to operate so-called electrostatically in such a way that the predetermined voltage levels in the separate treatment blocks of a mould are substantially constant through the entire spraying cycle. On the other hand, it is also possible to make the control unit dynamical, such that certain process. parameters are changed continuously or by way of an on/off principle during the course of spraying. Another essential benefit gained by the apparatus of the invention is that, even when processing a multi-component material, it is possible to use just one spraying cycle to achieve a completely finished end result, which, thus, does not necessarily require any kind of finishing operations when using properly blended process materials, regarding e.g. colouring or other mechanical/physical characteristics, such as surface tension, surface strength or the like.
In the following specification, the invention will be described in more detail with reference made to the accompanying drawings, in which